This invention relates to a hydrophilic sponge, adapted for medical and particularly surgical usage, comprising the reaction product of polyvinyl alcohol and formaldehyde. The sponge when wet with body fluids has a smooth and non-abrasive soft texture, is lint free, even when used abradably, is of exceptionally high fluid holding capacity, is compressible, flexible and resilient.
Medical sponges have many fluid absorbing applications including bandages for cuts and bruises, sanitary napkins for feminine hygiene, diagnostic swab "mailers" upon which bacteria can be cultured, general surgical sponges and specialty surgical sponges adapted for orthopedic, vascular, plastic, eye, ear, nose and throat use, among other known applications. As is described in U.S. Pat. No. 3,566,871, surgical sponges are used to remove body fluids such as blood, serum, plasma, lymph, spinal fluid, tissue fluid, urine, sweat, bile juice, and digestive juice. In the practice of surgery following an initial incision, it is customary to blot the incision and the adjacent area with sponges to remove blood and other fluids emanating from that incision. During internal surgery, for example, when operating in the thoracic cavity or abdominal cavity, sponges are used both to absorb blood and to isolate various organs from the operating field. The latter is accomplished by packing those organs with sponges to restrain them from interfering with the operation. The packing sponges are customarily pre-moistened in saline solution to prevent drying out organs or tissue with which they come into contact.
The sponge most commonly used today is a cellulose derived pad that may be of woven cotton, nonwoven cellulose or a felt made of rayon. However, cellulose pads tend to fragment and may shed lint thereby depositing biologically incompatible foreign substances in critical sites which can lead to the formation of brain or pulmonary emboli. As such, the fragments may also serve as a carrier for bacteria present in nonsterile areas of the operating room. The cellulose dust generated by opening a package of gauze pads may also lay down on the surface of open vessels of injectable solutions in the operating room enabling cellulose fragments to enter the blood stream directly. The gauze pad fragments left on internal organs also give rise to an adverse inflammatory reaction in the body, such as granulomater or adhesions.
Furthermore, gauze pads are known to be abrasive especially when dry. During use, as they absorb blood and body fluids, they tend to ball up and become increasingly harder and less pliable and therefore exhibit correspondingly increased abrasiveness. That is true notwithstanding the fact that the gauze pads were pre-moistened with saline solution. Since surgical pads may have to be moved or repositioned during an operation, abrasiveness of the pad can lead to trauma and inflammation.
Gauze pads used in surgery have the further disadvantage that they may not readily be shaped other than square or rectangular. That is due to their property of fraying and tendency to shed fragments. Thus, a surgeon cannot readily cut gauze pads to adapt them to a particular use.
Another problem with gauze pads is that they do not have a high capacity for holding fluid which increases the number of pads needed for a given medical procedure. In general their fluid holding capacity is limited to about 6 to 7 times the weight of the dry gauze. It would be greatly desirable to provide a pad capable of absorbing more than about 20 times its weight so as to reduce the need for replacing the pads during an operation.
The aforementioned U.S. Pat. No. 3,566,871 seeks to resolve the above problems associated with the use of gauze pads by means of a sponge made of polyurethane. That sponge is described as overcoming, for the most part, the problems of the gauze pad. The polyurethane sponge pad apparently does overcome some of the deficiencies of the gauze pad but in doing so it also appears to generate new problems of its own. For example, the polyurethane sponge described therein is impregnated with a hydrophilic surfactant absorbed into the sponge pores. The difficulty with that sponge, is that it contains a surfactant designed to render it artificially hydrophilic since polyurethane generally is otherwise hydrophobic. Those surfactant agents or substances have a tendency to leach out in the bloodstream. Although designed to absorb blood and body fluids upon contact, without compression, the fact remains that during the course of an operation, limitations of working space within the body make it highly unlikely that the surgeon will completely avoid making some contact with the sponges. Thus, when viewed pragmatically, particularly in the course of surgery, some compression of the sponges used is likely to occur. The significance of that compression, even if occasional, is that upon such compression the polyurethane sponge will release not only the blood and fluids absorbed, but also surfactant. That surfactant is a foreign substance and the body reacts to it just as it would to any foreign substance. Although described as substantially free of toxicity, it is in fact, and to varying degrees, toxic.
The polyurethane sponge also suffers from other deficiencies. Among its shortcomings is the fact that it remains somewhat abrasive. If particles should break off from the main sponge, the particles are not biocompatible. The sponge is not compressible for packaging and handling purposes. It does not completely resolve the problem of linting, is non-compressible, is friable, may yellow with age, and it is difficult to control the pore size of the sponge. Pore size control is of particular significance for precision work such as for neurosurgical or opthalmic surgical sponge instruments. For example, in opthalmic surgery it is most important that the sponge used to pick up blood and vitrous fluids which is commonly in the shape of a sponge-tipped spear and generally referred to as an "eye spear" has a definite smooth, predictable boundary. If an eye spear has large pores, its cut edge could have a half-moon shaped or swiss-cheese-like indentation. That would adversely affect the precision with which the eye surgery could be performed, e.g. the fine sutures used in eye surgery may get caught in the rough edges of the sponge. Thus a small uniform pore size distribution is desirable for eye surgical sponges. On the other hand, if a sponge is to be used for routine surgical procedures, e.g. soaking blood, a larger pore size would be acceptable.
One characteristic common to virtually all known surgical sponges used in internal surgery is that they are tagged with thin strips of radiopaque markers. Such radiopaque markers are visible by X-ray fluoroscopy. Thus, following surgery, a patient may be X-rayed to locate or help determine the presence of a sponge that may have slipped from view in the operative field. The difficulty with such radiopaque markers is that their visibility is limited by their size. X-ray opaque strips used on present gauze pads are made by mixing 6-12% barium sulfate with a resin such as polyethylene and extruding the resultant composition into a rod of about 1/16-inch diameter. The rod is heat sealed to the pad surface. The pad then is folded 12 to 15 times with the strip contained therein. As a practical matter, it would greatly facilitate determining the location of a sponge if the entire sponge was radiopaque and thus visible upon X-ray. However, this improved radiopacity must be achieved without altering fluid capacity or leaching of the radiopaque material from the sponge so that a foreign body toxic reaction is avoided.
Reaction products of polyvinyl alcohol and formaldehyde also have been used to produce sponge material, which material has been used as a washcloth, synthetic chamois skin, and the like. U.S. Pat. No. 2,609,347 describes sponges made by reacting polyvinyl alcohol and formaldehyde. The sponges made as described in said patent are intended for use as washcloths or chamois skin. Past efforts to use the sponge clinically for skin grafts and implantation in living tissue proved for the most part unsuccessful. This result is primarily due to possible toxic residues leaching from the sponge resulting in unreliable biocompatibility.
Furthermore, the sponges produced by the process described in U.S. Pat. No. 2,609,347 are undesirable for surgical sponges since they are not characterized by a pore geometry and size necessary for fast wicking, high liquid holding capacity and precision sponge instrument design. Fast wicking is highly desirable, since a sponge, in the dry state, is relatively abrasive and it is desirable to minimize abrasiveness quickly. The process described in this patent also is deficient for surgical purposes since no means are provided for assuring that the sponges produced will expand uniformly. This characteristic is essential since the utility of a medical sponge instrument is also dependent upon its predictable shape during use. This requires that a dry sponge, which is cut and compressed to a desired shape prior to use retains that shape and expands to a predictable volume during liquid absorption. Furthermore, the sponge described in this patent is undesirable since its liquid holding capacity is only in the order of 10 to 13 times the weight of the sponge.
Accordingly, it would be desirable to provide a soft non-toxic uniformly expandable medical sponge having a high fluid holding capacity and fast wicking which is lint free, even when cut or trimmed to a smaller size. Furthermore, it would be desirable to provide a medical sponge which is non-abrasive to delicate tissue and is capable of being rendered homogeneously radiopaque without incorporating a leachable X-ray opaque material into the sponge. In addition, it would be desirable to provide such a sponge which can be formed in a manner such that the size and geometry of the sponge pores can be regulated to conform to the desired pore size distribution required for fast wicking, high liquid holding capacity, and precision design. Also, it would be desirable to provide a sponge, which when expanded by virtue of liquid absorption, will expand to a predictable shaped volume.